Organocatalytic [4+2] Benzannulation between 1,4-dithiane-based enal and nitroolefins to access 2-nitrobiaryls

Abstract

A simple method for constructing unsymmetrical 2-nitrobiaryls has been developed between substituted 1,4-dithiine-2-carbaldehyde and nitroolefins under metal-free conditions. To gain the advantage of the HOMO-raising effect of temporary substitutions on in situ generated dienamine intermediate, the present protocol established [4+2] benzannulation of 1,4-dithiane-tethered enals with nitroolefin. Further, easy unmasking of 1,4-dithiine units results in a benzannulation product like that of unsubstituted enals, which are difficult to access. Several 2-nitrobiaryls have been accessed with moderate to good yields and with promising synthetic applications.